1. Field of the Invention
The cyclodextrins (CD's), also known as cycloamyloses and Schardinger dextrins, are a series of cyclic oligosaccharides produced by the action on starch of cyclodextrin glycosyl transferases obtained from several known microorganisms. CD's are composed of six or more D-glucopyranose units in the C1 chair conformation connected by alpha-(1,4) linkages to form a torus, or doughnut-shaped polymer [Bender et al., Cyclodextrin Chemistry, Springer-Verlag, New York (1978)]. Each homolog is designated by a Greek letter indicating the number of monomer units in the compound. The alpha-, beta-, and gamma-CD's, which contain, respectively, 6, 7, and 8 D-glucose units, preponderate over any higher molecular weight CD's that might form during enzymatic digestion of starch.
In recent years, especially in Europe and Japan, there has been increased interest in CD's, because of the utility and scope of their complexation reactions. In particular, the pharmaceutical, cosmetic, toiletry, food, and agrochemical industries have directed attention to these compounds. A continuing problem is the need for effective methodology for separating, on a preparative scale, CD mixtures or mixtures of products formed through derivatization of CD's. This invention relates to an easy, practical, economical means for fractionating CD's and separating them from the bulk of complex reaction mixtures.
2. Description of the Prior Art
The separation of mixtures of alpha-, beta-, and gamma-CD's, especially those mixtures of CD's contained in crude starch digests, has often been accomplished by selective precipitation by appropriate organic compounds such as tetrachloroethylene, tetrachloroethane, p-cumene, cyclohexane, fluorobenzene, and anthracene [Cramer et al., Chem. Ber. 91(2): 308-310 (1958); Freudenberg et al., Ann. 518: 102-108 (1935); French et al., JACS 71(1): 353-356 (1949)]. Separations by partition chromatography on cellulose columns with ternary solvents for development [Lammers, Starke 19(3): 70-73 (1967)], high-temperature cellulose column chromatography [French et al., Arch. Biochem. Biophys. 111(1): 153-160 (1965)], gel-permeation chromatography on crosslinked dextran [Zsadon et al., Starke 30(8): 276-279 (1978); Carter et al., Anal. Biochem. 39(2): 521-527 (1971)], and adsorption chromatography on charcoal with gradient elution (butanol-water) [Lammers, J. Chromatog. 41(3-4): 462-466 (1969)], have all been at least moderately effective. Thin-layer [Wiedenhof, J. Chromatog. 15(1): 100-102 (1964)], circular paper [Cramer et al. Ann. 595(2): 81-100 (1955)], and high-performance liquid [M. Szilasi et al., In First International Symposium on Cyclodextrins, J. Szejtli (ed.), D. Reidel Publishing Co., Boston, 1982, pp. 61-68; B. Zsadon et al., J. Chromatog. 172: 490-492 (1979)] chromatography have been applied as analytical tools. However, there have been no reported applications of affinity chromatography for analyzing or separating mixtures of CD's.